Traynor YBA-1 But Which One?

[Stevem]

The cab kinda looks home grown to me?

[Blindog]

This PDF has several versions of the YBA-1, from the early tube rectified to the later. I believe mine is a '68 as well. I found a schematic in that package that was close to mine. With a few tweaks it can be very close to a tweed Bassman. Off the top of my head, the 4M volume pots and 100K mixer resistors were the first things I changed. I ended up rebuilding the board after I found it had become conductive. Ended up doing mostly a Marshall 1987 circuit. Love it!


Mark

[dorrisant]

After studying all of the posted info and closer inspection I am pretty sure it is a '69. The two volume pots are stamped '69.

Looking at the pdf Blindog posted, the preamp is the same as the schematic on page 4, all the way up to the power tube bias. The power section from there on to the output and the power supply are the same as page 6, including the bias resistors. No real need to try to draw it up. BTW... What would be wrong with removing the 180 ohm resistor across the output terminals?

I have decided to rebuild the board with a new eyelet board. I will use all the original parts except for the electrolytics. I'm gonna put in some extra space in case i decide to separate the cathodes of V1. I don't want to change the amp too much, but I will if it makes it any better.

I don't know what to think of the OT that came with it... It has an odd set of leads that come out of the side with the secondaries. The secondaries (black & green) show about a 28:1 turns ratio. 13.77 vac into the primaries gives 0.49 vac on the black and green leads. The others are gray, yellow and orange. They all show some voltages when the primary is supplied. I was hoping that they were the other unused secondaries but they show no continuity with the black and green. Any ideas? That Hammond replacement OT looks tempting, all but the price.

Thanks again for all the help and suggestions.
Tony

[dorrisant]

Ok, I replaced the board with one that has some additional space so I could split the common cathode set on V1. The two Orange Drops are .47uF and .22uF in parallel to get close enough to the .68uF bypass cap value on channel 2.

I also put in an adjustable bias and used individual screen grid resistors on the power tubes. I replaced all electrolytic caps, upping the can caps to 50-50uF. I figured it could use fresh diodes as well.

I used 1M volume pots with the on-off switch built in. This is an experiment to try to isolate the channels by taking them out of the circuit just before the mix resistors. I think this should work just fine, we shall see.

The few changes in resistors are pretty obvious (in blue), other than that I tried to keep it close to stock.

I'm not sure how to hook up the Presence control... the pot is 5k instead of the 25k that was in there. Could someone help me here with a diagram? I'm trying to go for the suggested mod - the one with the "scratchy" 5k pot... I hear that it sounds the best... don't know if i have it wired correctly or not.

Now it is time to blow the chassis out with compressed air and put it on the variac for some cap forming. Let me know if any of you see anything wonky.

Tony

[Smokebreak]

Looks great man! Hook up the presence like the 5F6A and you should be golden. I like that one too. Better range. Make sure and ground the 5k pot, it IS your tail resistor.

[dorrisant]

Thanks! Will do on the ground... It came up on the Variac just fine. Next, tubes.

Tony

[dorrisant]

When I was running it up on the Variac, I saw the preamp plates were getting too high. I don't know what the plates are supposed to actually be. I looked at another schematic and saw that there was another 10k dropping resistor and a 10uF cap at V1 B+ so I went ahead and popped it in, right there by the plate resistors. The 10k dropper is at the other end of the board. Had just enough room... and it still looked good.

Ran it the rest of the way up... then again with the tubes, adjusted the bias. Good to go. Hooked it up to my test cab and let it rip. Holy cow!!! Thunderously good!! The new volume pots with the switches seem to work great. I am able to completely disconnect either channel without any extra noise. When you turn one channel off while playing, it sounds like you've switched in a big bypass cap. Lots more gain. Both channels sound as advertised. I'm gonna be monkeying around with this one for a while... I can already tell...

Thanks again for the help,
Tony

[xtian]

I'm gonna be monkeying around with this one

That's my job! You owe me $0.50.

Looks great!